From 7b00a1faa357850efcc4f5b17dfeb431db2b5e9d Mon Sep 17 00:00:00 2001
From: Jude Nelson <judecn@gmail.com>
Date: Mon, 20 Nov 2023 12:20:49 -0500
Subject: [PATCH 1/3] feat: side-car to watch and report estimated sats/vbyte

---
 contrib/side-cars/fee-estimate.sh | 211 ++++++++++++++++++++++++++++++
 1 file changed, 211 insertions(+)
 create mode 100755 contrib/side-cars/fee-estimate.sh

diff --git a/contrib/side-cars/fee-estimate.sh b/contrib/side-cars/fee-estimate.sh
new file mode 100755
index 000000000..1682c3fe0
--- /dev/null
+++ b/contrib/side-cars/fee-estimate.sh
@@ -0,0 +1,211 @@
+#!/bin/bash
+
+####################################
+# Usage
+# 
+# $ ./fee-estimate.sh
+# 161
+# 
+# $ ./fee-estimate.sh test; echo $?
+# 0
+####################################
+
+set -uoe pipefail
+
+function exit_error() {
+   echo >&2 "$@"
+   exit 1
+}
+
+####################################
+# Dependencies
+####################################
+# Dependencies
+for cmd in curl jq bc sed date grep; do
+   command -v "$cmd" >/dev/null 2>&1 || exit_error "Command not found: '$cmd'"
+done
+
+
+####################################
+# Functions
+####################################
+
+# Convert a fee/kb to fee/vbyte.
+# If there's a fractional part of the fee/kb (i.e. if it's not divisible by 1000),
+# then round up.
+# Arguments:
+#   $1 -- the fee per kb
+# Stdout: the satoshis per vbyte, as an integer
+# Stderr: none
+# Return:
+#   0 on success
+#   nonzero on error
+function fee_per_kb_to_fee_per_vbyte() {
+   local fee_per_kb="$1"
+   local fee_per_vbyte_float=
+   local fee_per_vbyte_ipart=
+   local fee_per_vbyte_fpart=
+   local fee_per_vbyte=
+
+   # must be an integer
+   if ! [[ "$fee_per_kb" =~ ^[0-9]+$ ]]; then
+      exit_error "Did not receive a fee/kb from $fee_endpoint, but got '$fee_per_kb'"
+   fi
+
+   # NOTE: round up -- get the fractional part, and if it's anything other than 000, then add 1
+   fee_per_vbyte_float="$(echo "scale=3; $fee_per_kb / 1000" | bc)"
+   fee_per_vbyte_ipart="$(echo "$fee_per_vbyte_float" | sed -r 's/^([0-9]*)\..+$/\1/g')"
+   fee_per_vbyte_fpart="$(echo "$fee_per_vbyte_float" | sed -r -e 's/.+\.([0-9]+)$/\1/g' -e 's/0//g')"
+   fee_per_vbyte="$fee_per_vbyte_ipart"
+   if [ -n "$fee_per_vbyte_fpart" ]; then
+      fee_per_vbyte="$((fee_per_vbyte + 1))"
+   fi
+
+   echo "$fee_per_vbyte"
+   return 0
+}
+
+# Determine satoshis per vbyte
+# Arguments: none
+# Stdout: the satoshis per vbyte, as an integer
+# Stderr: none
+# Return:
+#   0 on success
+#   nonzero on error
+function get_sats_per_vbyte() {
+   local fee_endpoint="https://api.blockcypher.com/v1/btc/main"
+   local fee_per_kb=
+
+   fee_per_kb="$(curl -sL "$fee_endpoint" | jq -r '.high_fee_per_kb')"
+   fee_per_kb_to_fee_per_vbyte "$fee_per_kb"
+   return 0
+}
+
+# Update the fee rate in the config file.
+# Arguments:
+#   $1 -- path to the config file
+#   $2 -- new fee to write
+# Stdout: (none)
+# Stderr: (none)
+# Returns:
+#   0 on success
+#   nonzero on error
+function update_fee() {
+   local config_path="$1"
+   local fee="$2"
+   sed -i -r "s/satoshis_per_byte[ \t]+=.*$/satoshis_per_byte = ${fee}/g" "$config_path"
+   return 0
+}
+
+# Poll fees every so often, and update a config file.
+# Runs indefinitely.
+# If the fee estimator endpoint cannot be reached, then the file is not modified.
+# Arguments:
+#   $1 -- path to file to watch
+#   $2 -- interval at which to poll, in seconds
+# Stdout: (none)
+# Stderr: (none)
+# Returns: (none)
+function watch_fees() {
+   local config_path="$1"
+   local interval="$2"
+
+   local fee=
+   local rc=
+
+   while true; do
+      # allow poll command to fail without killing the script
+      set +e
+      fee="$(get_sats_per_vbyte)"
+      rc="$?"
+      set -e
+
+      if [ $rc -ne 0 ]; then
+         echo >&2 "WARN[$(date +%s)]: failed to poll fees"
+      else
+         update_fee "$config_path" "$fee"
+      fi
+      sleep "$interval"
+   done
+}
+
+# Unit tests
+function unit_test() {
+   local test_config="/tmp/test-miner-config-$$.toml"
+   if [ "$(fee_per_kb_to_fee_per_vbyte 1000)" != "1" ]; then
+      exit_error "failed -- 1000 sats/kbyte != 1 sats/vbyte"
+   fi
+
+   if [ "$(fee_per_kb_to_fee_per_vbyte 1001)" != "2" ]; then
+      exit_error "failed -- 1001 sats/vbyte != 2 sats/vbyte"
+   fi
+
+   if [ "$(fee_per_kb_to_fee_per_vbyte 999)" != "1" ]; then 
+      exit_error "failed -- 999 sats/vbyte != 1 sats/vbyte"
+   fi
+
+   echo "satoshis_per_byte = 123" > "$test_config"
+   update_fee "$test_config" "456"
+   if ! grep 'satoshis_per_byte = 456' >/dev/null "$test_config"; then
+      exit_error "failed -- did not update satoshis_per_byte"
+   fi
+  
+   echo "" > "$test_config"
+   update_fee "$test_config" "456"
+   if grep "satoshis_per_byte" "$test_config" >/dev/null; then
+      exit_error "failed -- updated satoshis_per_byte in a config file without it"
+   fi
+
+   rm "$test_config"
+   return 0
+}
+
+####################################
+# Entry point
+####################################
+
+# Main body
+# Arguments
+#   $1: mode of operation.  Can be "test" or empty
+# Stdout: the fee rate, in sats/vbte
+# Stderr: None
+# Return: (no return)
+function main() {
+   local mode="$1"
+   local config_path=
+   local interval=
+
+   case "$mode" in
+      "test")
+         # run unit tests
+         echo "Run unit tests"
+         unit_test
+         exit 0
+         ;;
+      "watch")
+         # watch and update the file
+         if (( $# < 3 )); then
+            exit_error "Usage: $0 watch /path/to/miner.toml interval_in_seconds"
+         fi
+         
+         config_path="$2"
+         interval="$3"
+
+         watch_fees "$config_path" "$interval"
+         ;;
+
+      "")
+         # one-shot
+         get_sats_per_vbyte
+         ;;
+   esac
+   exit 0
+}
+
+if (( $# > 0 )); then
+   # got arguments
+   main "$@"
+else
+   # no arguments
+   main ""
+fi

From 29e31cd43a531e4d9464a030c49a43a6f5a013e4 Mon Sep 17 00:00:00 2001
From: Jude Nelson <judecn@gmail.com>
Date: Mon, 20 Nov 2023 12:30:57 -0500
Subject: [PATCH 2/3] chore: more usage docs

---
 contrib/side-cars/fee-estimate.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/contrib/side-cars/fee-estimate.sh b/contrib/side-cars/fee-estimate.sh
index 1682c3fe0..672f237df 100755
--- a/contrib/side-cars/fee-estimate.sh
+++ b/contrib/side-cars/fee-estimate.sh
@@ -3,9 +3,14 @@
 ####################################
 # Usage
 # 
+# $ # one-shot fee-rate calculation
 # $ ./fee-estimate.sh
 # 161
 # 
+# $ # Check fees every 5 seconds and update `satoshis_per_byte` in `/path/to/miner.toml`
+# $ ./fee-estimate.sh watch /path/to/miner.toml 5
+# 
+# $ # Run unit tests and report result (0 means success)
 # $ ./fee-estimate.sh test; echo $?
 # 0
 ####################################

From 0224b1a1dadbab0c49469cc8ca45afae0dfed909 Mon Sep 17 00:00:00 2001
From: Jude Nelson <judecn@gmail.com>
Date: Mon, 20 Nov 2023 15:42:58 -0500
Subject: [PATCH 3/3] chore: address PR feedback -- log HTTP errors and check
 that the config file exists

---
 contrib/side-cars/fee-estimate.sh | 50 +++++++++++++++++++++++++++----
 1 file changed, 45 insertions(+), 5 deletions(-)

diff --git a/contrib/side-cars/fee-estimate.sh b/contrib/side-cars/fee-estimate.sh
index 672f237df..e7810b488 100755
--- a/contrib/side-cars/fee-estimate.sh
+++ b/contrib/side-cars/fee-estimate.sh
@@ -25,8 +25,7 @@ function exit_error() {
 ####################################
 # Dependencies
 ####################################
-# Dependencies
-for cmd in curl jq bc sed date grep; do
+for cmd in curl jq bc sed date grep head tail; do
    command -v "$cmd" >/dev/null 2>&1 || exit_error "Command not found: '$cmd'"
 done
 
@@ -54,7 +53,7 @@ function fee_per_kb_to_fee_per_vbyte() {
 
    # must be an integer
    if ! [[ "$fee_per_kb" =~ ^[0-9]+$ ]]; then
-      exit_error "Did not receive a fee/kb from $fee_endpoint, but got '$fee_per_kb'"
+      return 1
    fi
 
    # NOTE: round up -- get the fractional part, and if it's anything other than 000, then add 1
@@ -70,6 +69,41 @@ function fee_per_kb_to_fee_per_vbyte() {
    return 0
 }
 
+# Query the endpoint and log HTTP errors gracefully 
+# Arguments:
+#   $1 endpoint to query
+# Stdout: the HTTP response body
+# Stderr: an error message, if we failed to query
+# Return:
+#   0 on success
+#   nonzero on error
+function query_fee_endpoint() {
+   local fee_endpoint="$1"
+   local response=
+   local http_status_code=
+
+   response="$(curl -sL -w "\n%{http_code}" "$fee_endpoint" || true)";
+   http_status_code="$(echo "$response" | tail -n 1)";
+   case $http_status_code in 
+      200)
+         ;;
+      429)
+         echo >&2 "WARN[$(date +%s)]: 429 Rate-Limited retreiving ${fee_endpoint}"
+         return 1
+         ;;
+      404)
+         echo >&2 "WARN[$(date +%s)]: 404 Not Found retrieving ${fee_endpoint}"
+         return 1
+         ;;
+      **)
+         echo >&2 "WARN[$(date +%s)]: ${http_status_code} Error retrieving ${fee_endpoint}"
+         return 1
+         ;;
+   esac
+   echo "$response" | head -n -1
+   return 0
+}
+
 # Determine satoshis per vbyte
 # Arguments: none
 # Stdout: the satoshis per vbyte, as an integer
@@ -81,8 +115,10 @@ function get_sats_per_vbyte() {
    local fee_endpoint="https://api.blockcypher.com/v1/btc/main"
    local fee_per_kb=
 
-   fee_per_kb="$(curl -sL "$fee_endpoint" | jq -r '.high_fee_per_kb')"
-   fee_per_kb_to_fee_per_vbyte "$fee_per_kb"
+   fee_per_kb="$(query_fee_endpoint "$fee_endpoint" | jq -r '.high_fee_per_kb')"
+   if ! fee_per_kb_to_fee_per_vbyte "$fee_per_kb"; then
+      return 1
+   fi
    return 0
 }
 
@@ -196,6 +232,10 @@ function main() {
          config_path="$2"
          interval="$3"
 
+         if ! [ -f "$config_path" ]; then 
+            exit_error "No such config file: ${config_path}"
+         fi
+
          watch_fees "$config_path" "$interval"
          ;;